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Reputation: 160

Storing pointers to C structures in R as integers

I've been working on using a C library from R by writing custom C-functions using the library's functionality, and then accessing these C-functions from R using the .C-Interface.

In some of the C-code, I allocate space for some custom structures and want to store pointers to them in R so I can use these structures in successive calls to .C. While toying around with the .C function, I noticed I can simply cast the pointer to the C-structure to int and store it in R as an integer. Passing this integer to later calls via .C works fine, I can keep track of my structures and use them without problems.

My somewhat naive question: what is wrong with storing these pointers in integers in R? It works fine so I'm assuming there has to be some downside, but I couldn't find any info on it.

Upvotes: 3

Views: 150

Answers (1)

Jan van der Laan
Jan van der Laan

Reputation: 8105

R's integers are 32 bits even on a 64 bits platform. Therefore, when working on a 64 bits system this won't work (the pointers will be 64 bits).

R has functionality for this. See the 'Writing R Extensions' manual, the section on 'External pointers and weak references'.

If you are willing to switch to c++ (which doesn't mean you have to rewrite all of your code), you can use the Rcpp package which makes this easier. See for example External pointers with Rcpp

Upvotes: 3

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